Due to the high water demand and unsustainable water resource, wastewater reclamation and wastewater treatment prior to discharge have become current important issues. Various treatment technologies, such as biological processes, have been improved as alternatives. In this study, the biological nitrogen removal system using pure-culture Bacillus licheniformis was developed and used as an internal treatment unit in an aquarium to improve the effluent quality for water reuse. The efficiencies for NH 4 -N and total nitrogen (TN) removal and the quality of treated water verified the occurrence of heterotrophic nitrification and aerobic denitrification; the nitrification rate was 0.84 mg/L-h and the denitrification rate was 0.62 mg/L-h. The maximal NH 4 -N and TN removal efficiencies were approximately 73% at the influent NH 4 -N of 30 mg/L. However, the other competitive heterotroph of Pseudomonas sp. was observed, which resulted in dramatically decreasing efficiencies and an enlarged ratio of carbon consumption and nitrogen removal. Although the overall performance of the B. licheniformis system was lower than the system using mixed-culture nitrifying and heterotrophic denitrifying microorganisms, the advantages of the B. licheniformis system were ease of operation and the fact that it is a land-limited treatment system. The research is ongoing to enhance performance and maintain excellent efficiency in a long-term operation.

Septic tanks in most developing countries are constructed without drainage trenches or leaching fields to treat toilet wastewater and /or grey water. Due to the short hydraulic retention time, effluents of these septic tanks are still highly polluted, and there is usually high accumulation of septic tank sludge or septage containing high levels of organics and pathogens that requires frequent desludging and subsequent treatment. This study aimed to reduce sludge accumulation in septic tanks by increasing temperatures of the septic tank content. An experimental study employing two laboratory-scale septic tanks fed with diluted septage and operating at temperatures of 40 and 30°C was conducted. At steady-state conditions, there were more methanogenic activities occurring in the sludge layer of the septic tank operating at the temperature of 40°C, resulting in less total volatile solids (TVS) or sludge accumulation and more methane (CH4) production than in the unit operating at 30°C. Molecular analysis found more abundance and diversity of methanogenic microorganisms in the septic tank sludge operating at 40°C than at 30°C. The reduced TVS accumulation in the 40°C septic tank would lengthen the period of septage removal, resulting in a cost-saving in desluging and septage treatment. Cost-benefit analysis of increasing temperatures in septic tanks was discussed.

Nitrate contamination of groundwater has become a serious issue affecting the quality of drinking water and human health. An energy-efficient, low-cost, and simple reactor was developed to remove nitrate via hydrogenotrophic denitrification (HD). Hydrogen (H 2 ) supply was optimized by using a continuous supply of hydrogen (1-15 mL/min). The results revealed that the optimal condition was 5 mL/min, which yielded a nitrogen removal efficiency of 86.4% and a hydrogen effectiveness of 199 mg-N/g-H 2 . In the subsequent experiment, an intermittent hydrogen supply was used to improve the hydrogen effectiveness and hydrogen consumption. Using a cycle with a short period of hydrogen supply (3 min with hydrogen supply and 7 min with no hydrogen supply), excellent nitrogen removal efficiency (96.5%) was achieved, and the hydrogen effectiveness increased to 744 mg-N/g-H 2 . Furthermore, bacteria belonging to the Proteobacteria phylum and Betaproteobacteria class were the major components of the microbial community. However, Hydrogenophaga spp. (39.3%) was dominant under the continuous system, whereas Thauera spp. (58.5%) was the most abundant species under the intermittent system. In this study, Hydrogenophaga spp., Thauera spp., and Rhodocyclaceae, which were responsible for HD, afforded in efficient nitrogen removal from groundwater.

On-site sanitation systems are typically installed to treat grey and toilet wastewaters in areas without sewer and centralized treatment systems. It is well known that, due to inappropriate design and operation, treatment performance of these systems in developing countries is not satisfactory in the removal of pathogens and organic matters. This research aimed to investigate the hydraulic conditions occurring in some on-site sanitation systems and the effects of hydraulic retention times (HRTs) on the system performance. The experiments were conducted with a laboratory-scale septic tank (40L in size) and an actual septic tank (600L in size), to test the hydraulic conditions by using tracer study with HRTs varying at 12, 24 and 48 hr. The experimental results showed the dispersion numbers to be in the range of 0.017-0.320 and the short-circuit ratios in the range of 0.014-0.031, indicating the reactors having a high level of sort-circuiting and approaching complete-mix conditions. The removal efficiency of BOD5 was found to be 67% and the k30 values for BOD5 was 2.04 day -1. A modified complete-mix model based on the relationship between BOD5 removal efficiencies and HRTs was developed and validated with actual-scale septic tank data having a correlation coefficient (R 2 ) of 0.90. Therefore, to better protect our environment and minimizing health risks, new generation toilets should be developed that could minimize short-circuiting and improving treatment performance.

The physicochemical and biological characteristics of milli-microbubbles were compared to evaluate their performance on hydrogenotrophic denitrification (HD) for groundwater treatment in remote areas. The hydrogen supply was controlled at 1.14 L/d with 40 mgN/L of NO 3 -N. The microbial community structure in two bubble reactors was investigated by high throughput sequencing. Microbubbles enhanced biodegradation in the HD system, providing a maximum nitrogen removal efficiency of 99%. Approximately 50% of total hydrogen was utilized for biological nitrate removal with the highest hydrogen effectiveness achieved at 1.21 g N/g H 2 . In contrast, millibubbles achieved less than 10% efficiency and 9.9% of total hydrogen was consumed for biological nitrogen removal. Thauera spp., Hydrogenophaga spp. and Rhodocyclaceae of Proteobacteria phylum were the dominant bacteria in the microbubble reactor, whereas Methyloversatilis spp. was dominant in the millibubble reactor, in which a relatively low amount of hydrogen (0.6 mg/L) was dissolved. The differences can be attributed to the higher hydrogen transfer efficiency (45×10 -3 s -1 ) and lower rising velocity (0.31 mm/s) of the microbubbles system than the millibubbles system (2×10 -3 s -1 and 480 mm/s). The micro-hydrogen bubble technology affords increased hydrogen effectiveness, reduced energy consumption, and modified system design. Therefore, it is more appropriate for enhancing HD.